Such electrical units, in particular in the form of programmable logic controllers, are generally known and serve, for example, to monitor, control and regulate industrial production processes. Sensor data or switching signals are e.g. evaluated by the PLC by means of the measurement input or by means of a plurality of measurement inputs for this purpose.
The measurement inputs require a predefined minimum voltage and/or a predefined minimum current of the electrical input signal to detect a high level. The high level can, for example, indicate that a switch has been closed.
Due to the required minimum voltage and the required minimum current, the electrical input signal has a not insubstantial electric energy that has to be dissipated in the unit/PLC and is e.g. converted into heat. A high electrical power can thus in particular result on a use of a plurality of measurement inputs that has to be converted into heat and has to be led off from the electrical unit. This can have the result at higher environmental temperatures, for example, that all the measurement inputs of the unit or of the PLC can no longer be used (“derating”).
A measurement transducer is known from EP 1 022 702 A2 that uses an electrical measurement signal for the energy supply of its operation. A further sensor self-supplying with energy is known from U.S. Pat. No. 6,018,700 A.